1. Field of the Invention
The present invention relates to a micro-blower suitable for conveying compressive fluid, such as air.
2. Description of the Related Art
Small electronic devices, such as notebook personal computers and digital AV devices, are equipped with a blower for efficiently removing heat generated inside. It is important and necessary that such a blower for cooling purposes be a small and low-profile blower which consumes less power and has a low noise level.
A piezoelectric micro-blower is disclosed in International Publication No. WO 2008/069266. FIGS. 1A-1E illustrate a cross-sectional structure and an operation of a piezoelectric micro-blower according to International Publication No. WO 2008/069266. The piezoelectric micro-blower includes a blower body 1 and a diaphragm 2 fixed at its periphery to the blower body 1. A piezoelectric element 3 is attached to the center of the backside of the diaphragm 2. A blower chamber 4 is formed between a first wall 1a of the blower body 1 and the diaphragm 2. The first wall 1a is provided with a first opening 5a that faces the center portion of the diaphragm 2.
Applying a voltage to the piezoelectric element 3 causes the diaphragm 2 to bend and change the distance between the first opening 5a and the diaphragm 2. The blower body 1 has a second wall 1b spaced from the first wall 1a. The second wall 1b is disposed opposite the blower chamber 4 with the first wall 1a interposed therebetween. The second wall 1b is provided with a second opening 5b that faces the first opening 5a. There is an inflow passage 7 between the first wall 1a and the second wall 1b. The inflow passage 7 leads to the outside at its outer end, and connects to the first opening 5a and the second opening 5b at its inner end.
FIG. 1A illustrates an initial state in which the diaphragm 2 is flat (i.e., in which no voltage is applied to the piezoelectric element 3). FIG. 1B illustrates the first quarter period of voltage application to the piezoelectric element 3. Since the diaphragm 2 bends downward, the distance between the first opening 5a and the diaphragm 2 increases and fluid is drawn through the first opening 5a into the blower chamber 4. This causes fluid in the inflow passage 7 to be partially drawn into the blower chamber 4.
In the next quarter period, when the diaphragm 2 returns to a flat state as illustrated in FIG. 1C, the distance between the first opening 5a and the diaphragm 2 decreases and the fluid is pushed out upward through the openings 5a and 5b. The fluid in the inflow passage 7 is drawn into this flow of fluid and flows upward together.
In the next quarter period, since the diaphragm 2 bends upward as illustrated in FIG. 1D, the distance between the first opening 5a and the diaphragm 2 decreases and the fluid in the blower chamber 4 is pushed out upward through the openings 5a and 5b at high speed.
In the next quarter period, when the diaphragm 2 returns to a flat state as illustrated in FIG. 1E, the distance between the first opening 5a and the diaphragm 2 increases. This causes fluid to pass through the first opening 5a and to be slightly drawn into the blower chamber 4. Because of inertial forces, however, the fluid in the inflow passage 7 continues to flow toward the center and in the direction in which the fluid is pushed out of the blower chamber 4. Then, the diaphragm 2 returns to the state of FIG. 1B and periodically repeats the actions shown in FIG. 1B to FIG. 1E.
In the piezoelectric micro-blower disclosed in International Publication No. WO 2008/069266, the wall that faces the center portion of the diaphragm is provided with the opening through which fluid is discharged. Therefore, the flow of fluid discharged through the opening is orthogonal to the piezoelectric micro-blower body.
However, with the structure from which compressive fluid is blown out in the direction orthogonal to the piezoelectric micro-blower body, even if the piezoelectric micro-blower itself is low profile, incorporating the piezoelectric micro-blower into a small and low-profile electronic device requires a vertical space to accommodate a flow of fluid which is blown out of the piezoelectric micro-blower. To enable fluid to flow horizontally within the housing of the electronic device, it is necessary to place the piezoelectric micro-blower vertically within the housing of the electronic device, or to provide an additional path to convert a vertical flow of discharged fluid into a horizontal flow. Since this eventually requires a vertical space, the piezoelectric micro-blower described above is not suitable for use with low-profile electronic devices.
As a solution to this, a side of the blower chamber of the piezoelectric micro-blower may be provided with an opening which allows fluid to be blown out to the side of the piezoelectric micro-blower body. However, it has been found that, in the piezoelectric micro-blower disclosed in International Publication No. WO 2008/069266 which is driven by a high frequency (e.g., in a barely audible frequency range of 15 kHz or higher or in an ultrasonic range) for prevention of drive noise, even if a side of the blower chamber is provided with an opening, no flow is generated and no fluid can be discharged to the side of the blower chamber.